Water management is becoming increasingly important, especially in water-scarce regions of the world, such as, for example, the Sun Belt in the U.S.A. In such regions, water taxes are usually high and, as such, there is a strong incentive to conserve and recover water.
Further, the management and treatment of sewage water is also becoming increasingly important due to costs associated thereto, environmental concerns, and stricter disposal criteria.
In areas were a municipal sewage system is not available, decentralized sewage systems such as, for example, septic tanks can be used. Such septic tanks usually have two compartments, with a first compartment receiving wastewater, and the second compartment outputting treated water to a leach field (also referred to as a drain field or seepage filed), which can span over a large area, for example, from 200 to 300 m2 for a three-bedroom house. Solids in the wastewater fall to the bottom of the first compartment while scum floats to the surface. A divider between the first and second compartments has an opening that allows scummy water to flow from the first to the second compartment where additional settling of solids in the water can occur. Anaerobic bacterial activity in the first and second compartments turns the solid deposits into sludge. The liquid present in the second compartment proceeds through the output of the septic tank, into the leach field where the impurities present in the water decompose in the soil.
Septic tanks must be cleaned out of their sludge on a regular basis. This typically involves a service truck pumping out the compartments of a tank and bringing the sludge to a municipal sewage treatment plant where the sludge is dumped and treated.
Characteristically, at such sewage treatment plants, the sludge mixes in with various pollutants and chemical generated by industries that also use the municipal sewage treatment plant. This causes sludge constituents to bind to these pollutants and chemicals to produce toxins that can be extremely difficult to eliminate. Typically, such toxins are eliminated by a costly burning process.
Decentralized sewage systems, other than septic tank systems, include those using rotating biological contactor disks (RBCDs) placed in a container vessel receiving sewage water. In such systems, space-apart disks are mounted on a rotating shaft and are partially submerged in sewage water. The RBCDs, which can be made of plastic, or of any other suitable material, accumulate bacteria over time. As the RBCDs rotate in the sewage water, the bacteria capture and digest matter of the sewage water. As the RBCDs rotates out the water and become exposed to air, the aeration facilitates the digestion of the matter by the bacteria formed on the RBCDs, which turns the sewage matter into biomass on the RBCDs. The treated sewage water is output from the vessel into a leach field.
After a period of time over which the RBCDs accumulate biomass, the biomass will break off from the RBCDs and fall to the bottom of the vessel. Regular pumping of the biomass accumulated at the bottom of the vessel is required.
Typically, the sewage water arrives directly into the vessel and dissolves therein. As such, a large number of RBCDs are required to ensure adequate treatment of the sewage water. Additionally, RBCD systems typically require an electrical motor to rotate the shaft and disks. The motor has to operate in a constantly humid environment and, as such, is prone to short and medium term failures, in which cases, the efficiency of the sewage treatment system falls off drastically.
It is, therefore, desirable to provide a decentralized sewage treatment that allows for separation of solid matter at the source, that has operational reliability, that has a small leach field footprint and that produces reusable water.